Reply With QuoteSounds to me like the hpfp is failing.
Fossicker
Hey all. Me again. So as the heading states i am getting a crank no fire issue at random some mornings. It'll start and die, then crank for about 5 seconds, maybe longer then fire as if nothing was wrong. No fault codes or anything. This can happen once a week or once after 3 days, but only first thing in the morning. So far only twice in the last 3 months, the car just wont start, even if i leave it for a while. So the only way It'll start is if i bleed air out of the bleeder at the top rear of the motor, It'll expell some air, the bam start and runs fine with still no fault codes. Now this can happen with any amount of fuel in the tank. I have replaced the fuel filter as it was due, i checked all the fuel line o-rings at the filter and they look really good. So the last time this happened i had my autel hooked up, and the fuel pressure was 1000kpa, when i bled the fuel system and it fired it, it was at about 18000kpa.
Is there a "common" place where i should check before i start stripping the back of the motor to check the lines to the High Pressure pump?
ChatterBox
SubscriberSounds to me like the hpfp is failing.
TopicToaster
SubscriberI had this. For me it was the crankshaft position sensor. You don’t get the fuel pressure because the engine isn’t seeing the CPS signal so it doesn’t command the HPFP. It might not be this but consider it. It took months before I finally broke down whilst driving and got an error logged. Prior to that it would just not start randomly.
2010 TDV6 3.0L Discovery 4 HSE
2007 Audi RS4 (B7)
Fossicker
The hpfp was already replaced by the previous owner.
I checked the crank sensor and it is working fine, tacho picks up at about 700rpm
But only when it is working?Originally Posted by Iherbst87
Crank angle sensors can be funny. Unless you checked it with a scope while the car wouldn't start, be hard to rule out, Jeff chased his for months before it finally threw a code
TopicToaster
SubscriberMy tacho was fine also, hence why I dismissed it initially
2010 TDV6 3.0L Discovery 4 HSE
2007 Audi RS4 (B7)
Fossicker
I checked it with my Autel when it was playing up and was working fine. I
need to bleed air out of the fuel bleed nipple before it will start, so i know its not electrical, it is sucking air somewhere
Put a gauge on that Schrader valve. Should be 7psi. When you cycle the key and at all times.. If it is. LPFP is working. Which means the only place it can suck air is inside the tank. Because anything after the pump is pressurized it'll leak not suck. maybe check and see if you can hear the LPFP when the car won't start. After first attempt. Ignition on only and see if you can hear it running.. These things are pretty good at self bleeding.. On a fuel filter change, I ignition on and off 3 times and it starts with a dry filter.
Fossicker
Cheers Josh. Yea i can hear the pump running and priming, even when it plays up. It seems odd if it is in the tank as it can even play up with a full tank? I haven't had the tank pump out before on one of these, but the previous owner replaced both pumps, he did not say why tho
ForumSage
The other way of looking at this is if there is a vacuum being created in the tank due to no air getting in to replace fuel going out.
DL
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